Vargas, a 13-year postal service veteran, is scheduled to be sentenced July 9. He faces up to 10 years in prison and a $250,000 fine.

He was indicted on the charge March 4.

Postal Service investigators discovered Vargas had used several Voyager cards to make unauthorized gasoline purchases totaling $17,829.39 from July 1, 2008, through Nov. 13, 2008, federal officials said.

Authorities said when officials confronted him about the purchases, Vargas said he either bought the gas for personal use or sold it at a discount to other people.

He would pump gasoline for others using a Voyager card and his personal identification number in exchange for a small cash fee.